JP7689835B2 - Optical system and imaging device - Google Patents

Description

The present invention relates to an optical system and an imaging device.

In recent years, imaging devices that add a zoom effect through image processing to the optical systems of digital input/output devices such as in-vehicle lenses and drone prime lenses have rapidly become popular. For this reason, the optical system must maintain high resolution from the center to the periphery at a wide angle.

For example, an optical system in which the signs of the refractive power of each lens are negative, negative, positive, positive, positive, negative, in order from the object side, and the half angle of view is 48 degrees is known (see, for example, Patent Document 1).

An optical system is also known in which, from the object side, the signs of the refractive power of each lens are negative, positive, positive, positive, negative, and positive, and the half angle of view is 50 degrees (see, for example, Patent Document 2).

An optical system is also known in which, from the object side, the signs of the refractive powers of the lenses are negative, negative, positive, positive, negative, and positive, and the half angle of view is 59 degrees (see, for example, Patent Document 3).

JP 2017-223755 A JP 2017-173807 A JP 2019-211598 A

However, the optical system described in Patent Document 1 has a problem in that the angle of view is small at 48 degrees, and the correction of field curvature is insufficient. Furthermore, the optical systems described in Patent Documents 2 and 3 have a problem in that the correction of field curvature and distortion in the peripheral area is insufficient.

One aspect of the present invention aims to realize a compact optical system and imaging device that can maintain high resolution from the center to the periphery of the screen at a wide angle.

In order to achieve the above object, an optical system according to one aspect of the present invention includes, in order from an object side, a first lens group and a second lens group having positive refractive power,
The first lens group includes, in order from the object side, a first lens L1 having a convex surface facing the object side and negative refractive power, and a second lens L2 having a meniscus shape and a concave surface facing the object side,
The total number of lenses is 5 to 10, and
An optical system that satisfies the following equation:
1.55<(C _L1r -C _L2f )×f<2.55 (1)
0.65<D _L12 /f<5.00 (2)
however,
C _L1r : Curvature of the lens surface on the image side of the first lens L1 C _L2f : Curvature of the lens surface on the object side of the second lens L2 f : Focal length of the optical system when focusing on infinity D _L12 : Distance on the optical axis between the lens surface on the image side of the first lens L1 and the lens surface on the object side of the second lens L2 when focusing on infinity

In order to achieve the above object, an optical system according to one aspect of the present invention includes, in order from an object side, a first lens group and a second lens group having positive refractive power,
The first lens group includes, in order from the object side, a first lens L1 having a convex surface facing the object side and negative refractive power, and a second lens L2 having a meniscus shape and a concave surface facing the object side,
the second lens group includes a third lens L3 having a positive refractive power and a stop on the image plane side of the third lens L3,
The total number of lenses is 5 to 10, and
An optical system that satisfies the following equation:
-2.3<f ₁₂ /f<-0.0 (3)
1.00<P _W12 ×f<4.00 (4)
-1.80<f ₁ /f<-0.10 (5)
however,
f ₁₂ : a composite focal length of the first lens L1 and the second lens L2, f: a focal length of the optical system when focused at infinity, P _W12 : (N _L1 −1)/R _L1r −(N _L2 −1)/R _L2f
N _L1 : refractive index at d line of the first lens L1 R _L1r : radius of curvature of the lens surface of the first lens L1 on the image side N _L2 : refractive index at d line of the second lens L2 R _L2f : radius of curvature of the lens surface of the second lens L2 on the object side f ₁ : focal length of the first lens L1

In order to solve the above problem, an imaging device according to one aspect of the present invention includes the optical system and an imaging element provided on the image plane side of the optical system, which converts an optical image formed by the optical system into an electrical signal.

According to one aspect of the present invention, it is possible to realize a compact optical system and imaging device that can maintain high resolution from the center to the periphery of the screen at a wide angle.

FIG. 2 is a diagram illustrating an optical configuration of the optical system of the first embodiment when focused on infinity. 4 is a diagram showing longitudinal aberration of the optical system of Example 1 when focused on an object at infinity. FIG. FIG. 11 is a diagram illustrating an optical configuration of the optical system of Example 2 when focused on infinity. FIG. 11 is a diagram showing longitudinal aberration of the optical system of Example 2 when focused on an object at infinity. FIG. 13 is a diagram illustrating an optical configuration of the optical system of Example 3 when focused on infinity. FIG. 13 is a diagram showing longitudinal aberration of the optical system of Example 3 when focused on an object at infinity. FIG. 13 is a diagram illustrating an optical configuration of the optical system of Example 4 when focused on infinity. FIG. 13 is a diagram showing longitudinal aberration of the optical system of Example 4 when focused on an object at infinity. FIG. 13 is a diagram illustrating an optical configuration of the optical system of Example 5 when focused on infinity. FIG. 13 is a diagram showing longitudinal aberration of the optical system of Example 5 when focused on an object at infinity. FIG. 23 is a diagram illustrating an optical configuration of the optical system of Example 6 when focused at infinity. FIG. 13 is a diagram showing longitudinal aberration of the optical system of Example 6 when focused on an object at infinity. FIG. 23 is a diagram illustrating an optical configuration of the optical system of Example 7 when focused on infinity. FIG. 13 is a diagram showing longitudinal aberration of the optical system of Example 7 when focused on an object at infinity. FIG. 23 is a diagram illustrating an optical configuration of the optical system of Example 8 when focused at infinity. FIG. 23 is a diagram showing longitudinal aberration of the optical system of Example 8 when focused on an object at infinity. FIG. 13 is a diagram illustrating an optical configuration of the optical system of Example 9 when focused on infinity. FIG. 13 is a diagram showing longitudinal aberration of the optical system of Example 9 when focused on an object at infinity. 1 is a diagram illustrating an example of a configuration of an imaging device according to an embodiment of the present invention.

The following describes an embodiment of an optical system and an imaging device according to one embodiment of the present invention. More specifically, this embodiment relates to an inexpensive and lightweight optical system suitable for use in optical systems of digital input/output devices such as vehicle-mounted lenses and drone single-focus lenses that use solid-state imaging elements. However, the optical system and imaging device described below are one aspect of the optical system and imaging device according to the present invention, and the optical system and imaging device according to the present invention are not limited to the following aspects. In this specification, a configuration expressed as "consisting of" means that the configuration is essentially the only one included. In addition, in this specification, a numerical range indicated by "to" means a numerical range including both ends of the numerical range.

1. Optical System 1-1. Optical Configuration An optical system according to an embodiment of the present invention is composed of a first lens group and a second lens group. The first lens group is composed of, in order from the object side, a first lens L1 having a convex surface facing the object side and negative refractive power, and a second lens L2 having a meniscus shape with a concave surface facing the object side. The second lens group has positive refractive power. The total number of lenses in the optical system is 5 to 10.

In this specification, a "lens group" may be defined as consisting of two or more lenses.

In this specification, the lens group may include a cemented lens. When the lens group includes a cemented lens, the number of lenses is the number of lenses that are each cemented together. An example of a cemented lens is a cemented lens in which multiple lenses are integrated together with no air gap between them. In this case, only the multiple lenses that make up the cemented lens are counted. Another example of a cemented lens is a cemented lens in which multiple lenses are integrated together and bonded together with a very thin adhesive that has a thickness that does not substantially affect the optical performance. In this case, the adhesive is not counted as a lens.

The lens group may also include a compound lens in which a single lens and resin are integrated together. For example, a compound lens in which a single lens and resin are integrated together is counted as one lens.

(1) First Lens Group The first lens group is the lens group disposed closest to the object in the optical system, and is made up of a first lens L1 and a second lens L2.

The first lens L1 is the lens arranged closest to the object in the optical system, has a convex surface facing the object, and has negative refractive power. The fact that the first lens L1 has negative refractive power is advantageous for widening the angle of view and reducing the front lens diameter (the diameter of the lens arranged closest to the object).

The second lens L2 is the second lens from the object side in the optical system, and is a meniscus-shaped lens with a concave surface facing the object side. The second lens L2 may have either negative or positive refractive power. It is preferable that the second lens L2 has negative refractive power, i.e., the first lens group is composed of two lenses with negative refractive power, because this realizes a wide angle of the optical system and can distribute the negative power between the first lens L1 and the second lens L2. By distributing the negative power between the first lens L1 and the second lens L2, coma aberration or field curvature can be distributed between the first lens L1 and the second lens L2.

(2) Second Lens Group The second lens group is a lens group arranged closer to the image surface than the first lens group. That is, the second lens group is a lens group including all lenses from the third lens L3 to the final lens Lf arranged closer to the image surface than the second lens L2. The second lens group has positive refractive power. The second lens group only needs to have positive refractive power as a whole, and it is preferable that the second lens group has at least two lenses having positive refractive power. It is preferable that the second lens group has positive refractive power from the viewpoint of appropriately correcting astigmatism generated in the first lens group and working advantageously for widening the angle.

The third lens L3 is the lens arranged closest to the object in the second lens group. It is preferable that the third lens L3 has a positive refractive power. It is preferable that the third lens L3 has a positive refractive power, from the viewpoint that the light beam diameter on the optical axis and in the periphery, which is enlarged by the first lens group having the first lens L1 having a negative refractive power, can be made smaller on the image plane side than the third lens L3. In addition, it is preferable that the third lens L3 has a positive refractive power, from the viewpoint that the distortion aberration or astigmatism generated in the first lens L1 is appropriately corrected by the refractive power of the second lens L2 located closer to the image side in the first lens group, and that it works in favor of high resolution or wide angle at the peripheral image height. In addition, it is preferable that the third lens L3 has a convex surface on the object side, from the viewpoint that the effect is enhanced.

The third lens L3 having negative refractive power is advantageous in dispersing the negative power required in the first lens group and suppressing the occurrence of coma aberration.

It is preferable that the third lens L3 has a convex surface on both the object side and the image side. It is preferable that the third lens L3 has a convex surface on both the object side and the image side from the viewpoint that when the third lens L3 has a strong power, it is possible to divide the power between the object side surface and the image side surface. By dividing the power between the object side surface and the image side surface, it is possible to divide the aberration correction between the object side surface and the image side surface. This has the effect of mitigating the sudden refraction of light rays and suppressing the occurrence of high-order aberrations.

It is preferable that the second lens group has at least one lens with negative refractive power. It is preferable that the second lens group has at least one lens with negative refractive power from the viewpoint of appropriately correcting chromatic aberration. It is also preferable that the second lens group has two or more lenses with positive refractive power. It is preferable that the second lens group has two or more lenses with positive refractive power from the viewpoint of appropriately correcting field curvature.

In the second lens group, it is preferable that one lens with negative refractive power is arranged on the object side of the lens with positive refractive power. Since arranging the entrance pupil position as close to the object side as possible leads to a reduction in size in the radial direction, such an arrangement is preferable from the viewpoint of realizing a compact optical system. For this reason, it is preferable to arrange a lens with negative refractive power on the object side of at least one lens with positive refractive power in the second lens group.

In addition, in the second lens group, from the viewpoint of realizing a compact optical system, it is preferable that the lens having negative refractive power has a refractive index at the d-line of greater than 1.65, and more preferably greater than 1.75.

In addition, in the second lens group, it is preferable to arrange a lens with negative refractive power on the image surface side of the lens with positive refractive power. Such an arrangement is preferable from the viewpoint of appropriately correcting chromatic aberration on the optical axis and in the vicinity of the optical axis. In particular, it is preferable to arrange a lens with positive refractive power on the object side of the lens with negative refractive power that is closest to the image surface in the second lens group.

The third lens L3, which is located closest to the object side in the second lens group, has a large difference in the incidence angle characteristics between off-axis light rays and on-axis light rays, and therefore has a higher correction effect for off-axis chromatic aberration than on-axis light rays. Therefore, it is preferable that the lens with positive refractive power included in the second lens group is made of relatively low dispersion glass. In addition, from the viewpoint of appropriately correcting chromatic aberration, the Abbe number at the d-line of the lens with positive refractive power included in the second lens group is preferably greater than 45, and more preferably greater than 48.

The final lens Lf is the lens in the second lens group closest to the image surface. It is preferable that the final lens Lf has a positive refractive power. It is preferable that the final lens Lf has a positive refractive power, because it can reduce the angle of incidence to the image surface, thereby reducing angle dependency. This also makes it possible to maintain a high amount of peripheral light up to the periphery.

The second lens group has a pair of compound lenses on the image surface side adjacent to the aperture, and the compound lenses preferably consist of one lens with positive refractive power and one lens with negative refractive power. The order of the lenses does not matter, as long as the two lenses are cemented together or the two lenses are adjacent to each other with an air gap between them. This configuration is preferable from the viewpoint of appropriately correcting axial chromatic aberration. In addition, the compound lenses are preferably cemented lenses from the viewpoint of reducing assembly sensitivity and realizing a shortened overall optical length of the optical system.

(3) Aperture The optical system preferably has an aperture. However, the aperture here refers to an aperture that defines the light beam diameter of the optical system, that is, an aperture that defines the F-number (Fno) of the optical system. The aperture is preferably disposed closer to the image surface side than the third lens L3 in the second lens group. Such an arrangement can reduce the aperture diameter, and can reduce the light beam diameter on the optical axis and in the periphery on the image surface side than the aperture. Reducing the light beam diameter on the optical axis and in the periphery is advantageous in suppressing the aberration correction between adjacent lenses. In addition, the aperture is preferably disposed between lenses having positive refractive power. Such an arrangement is preferable from the viewpoint of reducing the effective diameter of the lens on the object side and the image surface side of the aperture. In addition, it is possible to make the effective diameter of both the object side of the lens having positive refractive power on the object side of the aperture and the image surface side of the lens having positive refractive power on the image surface side of the aperture relatively small with respect to the aperture surface, which is advantageous in suppressing the aberration correction between adjacent lenses.

(4) Lens Group Configuration The optical system is composed of only two lens groups, a first lens group and a second lens group, in that order from the object side. No other lens groups are included between the first lens group and the second lens group. The optical system of this embodiment may further include optical elements other than the above lens groups, as long as the effects of this embodiment can be obtained.

The optical system has a total of 5 to 10 lenses. It is preferable that the optical system is made up of 5 or more lenses in order to achieve a wide angle and high resolution. It is also preferable that the optical system is made up of 10 or fewer lenses in order to achieve a compact optical system. As described above, the first lens group is made up of only two lenses, the first lens L1 and the second lens L2. Therefore, the second lens group is made up of 3 to 8 lenses.

1-2. Operation during focusing In this embodiment, focusing is performed by moving the entire optical system, and the spacing between each lens group does not change.

1-3. Equations Expressing the Conditions of the Optical System The optical system according to this embodiment employs the above-described configuration and preferably satisfies at least one of the following equations.

1.55<(C _L1r -C _L2f )×f<2.55 (1)
however,
C _L1r : Curvature of the lens surface of the first lens L1 on the image side C _L2f : Curvature of the lens surface of the second lens L2 on the object side f: Focal length of the optical system when focused at infinity

In formula (1), (C _L1r -C _L2f ) is equivalent to |C _L1r |+|C _L2f | and represents the sum of the curvature of the lens surface on the image side of the first lens L1 and the curvature of the lens surface on the object side of the second lens L2. Note that C _L1r is equivalent to the reciprocal (1/R _L1r ) of the curvature radius of the lens surface on the image side of the first lens L1, and C _L2f is equivalent to the reciprocal (1/R _L2f ) of the curvature radius of the lens surface on the object side of the second lens L2. Formula (1) indicates the sum of the curvature of the lens surface on the image side of the first lens L1 and the curvature of the lens surface on the object side of the second lens L2 normalized by the focal length at the time of focusing at infinity of the optical system. Satisfying formula (1) is preferable from the viewpoint of maintaining the field curvature at a moderate level and realizing a wide angle. If the lower limit of formula (1) is exceeded, the curvature of the lens surface on the image side of the first lens L1 and the curvature of the lens surface on the object side of the second lens L2 are small, so that the Petzval sum is large and it may be difficult to appropriately correct the image surface. Also, if the upper limit of formula (1) is exceeded, the field curvature may be overcorrected.

From the viewpoint of reducing the Petzval sum and appropriately correcting the field curvature, (C _L1r -C _L2f ) x f is more preferably greater than 1.60, and even more preferably greater than 1.63. Also, from the viewpoint of preventing excessive correction of the field curvature, (C _L1r -C _L2f ) x f is more preferably less than 2.40, and even more preferably less than 2.30.

It is preferable that the optical system according to this embodiment satisfies the following formula.
0.65<D _L12 /f<5.00 (2)
however,
D _L12 : The distance on the optical axis between the lens surface on the image side of the first lens L1 and the lens surface on the object side of the second lens L2 when the optical system is focused on infinity. f: The focal length of the optical system when focused on infinity.

Equation (2) is an equation for specifying the distance on the optical axis between the lens surface on the image side of the first lens L1 and the lens surface on the object side of the second lens L2 when the optical system is focused at infinity, relative to the focal length when the optical system is focused at infinity. Satisfying equation (2) is preferable from the viewpoint of maintaining a moderate level of field curvature, reducing the Petzval sum, and appropriately correcting the field curvature. If the lower limit of equation (2) is not satisfied, the Petzval sum will be large, making it difficult to appropriately correct the field curvature. Furthermore, if the upper limit of equation (2) is exceeded, the field curvature may be over-corrected.

From the viewpoint of reducing the Petzval sum and appropriately correcting the field curvature, D _L12 /f is more preferably greater than 0.67, even more preferably greater than 0.70, and particularly preferably greater than 0.75. Also, from the viewpoint of preventing excessive correction of the field curvature, D _L12 /f is more preferably less than 3.50, even more preferably less than 2.80, and particularly preferably less than 2.00.

It is preferable that the optical system according to this embodiment satisfies the following formula.
-2.3<f ₁₂ /f<-0.0 (3)
however,
_f12 : composite focal length of the first lens L1 and the second lens L2; f: focal length of the optical system when focused at infinity;

Equation (3) represents an equation in which the composite focal length of the first lens L1 and the second lens L2 is normalized by the focal length of the optical system when focused at infinity. Satisfying equation (3) is preferable from the viewpoints of achieving a large negative refractive power, realizing a wide angle, and appropriately correcting curvature of field. If the lower limit of equation (3) is not met, the negative refractive power is small, and it may be difficult to achieve a wide angle. Furthermore, if the upper limit of equation (3) is exceeded, it may be difficult to appropriately correct curvature of field.

From the standpoint of appropriately correcting the curvature of field, f ₁₂ /f is more preferably less than −0.3, further preferably less than −0.5, and particularly preferably less than −0.7.

It is preferable that the optical system according to this embodiment satisfies the following formula.
1.00<P _W12 ×f<4.00 (4)
however,
P _W12 :(N _L1 -1)/R _L1r -(N _L2 -1)/R _L2f
N _L1 : Refractive index at d line of the first lens L1 R _L1r : Radius of curvature of the lens surface on the image side of the first lens L1 N _L2 : Refractive index at d line of the second lens L2 R _L2f : Radius of curvature of the lens surface on the object side of the second lens L2 f : Focal length of the optical system when focused at infinity

Equation (4) represents the power of the air lens between the image-side lens surface of the first lens L1 and the object-side lens surface of the second lens L2. Satisfying equation (4) is preferable from the standpoint of increasing the influence of the power of the air lens and appropriately correcting the field curvature. If the lower limit of equation (4) is exceeded, the influence of the power of the air lens may be reduced. Furthermore, if the upper limit of equation (4) is exceeded, it may be difficult to appropriately correct the field curvature.

From the viewpoint of increasing the influence of the power of the air lens, P _W12 ×f is more preferably greater than 1.05. Also, from the viewpoint of appropriately correcting the field curvature, P _W12 ×f is more preferably less than 3.00, even more preferably less than 2.70, and particularly preferably less than 2.50.

It is preferable that the optical system according to this embodiment satisfies the following formula.
-1.80<f ₁ /f<-0.10 (5)
however,
_f1 : focal length of the first lens L1 f: focal length of the optical system when focused at infinity

Equation (5) represents an equation in which the focal length of the first lens L1 is normalized by the focal length of the optical system when focused at infinity. Satisfying equation (5) is preferable from the viewpoints of compensating for insufficient correction of field curvature, realizing a wide angle, reducing the effective diameter of the first lens L1, and keeping distortion small. If the lower limit of equation (5) is exceeded, the power of the first lens L1 becomes too weak, making it impossible to compensate for insufficient correction of field curvature, making it difficult to realize a wide angle, and the effective diameter of the first lens L1 may become too large. Furthermore, if the upper limit of equation (5) is exceeded, the power of the first lens L1 becomes too strong, making it difficult to keep distortion small.

From the viewpoints of compensating for insufficient correction of curvature of field, realizing a wider angle, and reducing the effective diameter of the first lens L1, f ₁ /f is more preferably greater than -1.76, even more preferably greater than -1.72, and particularly preferably greater than -1.68. Also, from the viewpoint of keeping distortion small, f ₁ /f is more preferably less than -0.80, even more preferably less than -1.20, and particularly preferably less than -1.30.

It is preferable that the optical system according to this embodiment satisfies the following formula.
-3.40<R _L2f /f<0.00 (6)
however,
R _L2f : Radius of curvature of the lens surface on the object side of the second lens L2 f : Focal length of the optical system when focused at infinity

Formula (6) represents an equation in which the radius of curvature of the object-side lens surface of the second lens L2 is normalized by the focal length when the optical system is focused at infinity. Satisfying formula (6) is preferable from the viewpoint of appropriately correcting the field curvature occurring on the object-side lens surface of the first lens L1, and enabling the angle of the chief ray to the first lens L1 to be increased in advance, thereby realizing a wide angle. If the lower limit of formula (6) is not met, the power of the object-side lens surface of the second lens L2 becomes too small, making it impossible to increase the angle of the chief ray in advance, and it may be difficult to realize a wide angle. Also, if the upper limit of formula (6) is exceeded, it may be difficult to appropriately correct the field curvature occurring on the object-side lens surface of the first lens L1.

From the viewpoint of realizing a wide angle, R _L2f /f is more preferably greater than -3.00, and even more preferably greater than -1.90. Also, from the viewpoint of appropriately correcting the field curvature generated on the object-side lens surface of the first lens L1, R _L2f /f is more preferably less than -0.10, and even more preferably less than -0.25.

It is preferable that the optical system according to this embodiment satisfies the following formula.
1.30<f _2g /f<2.70 (7)
however,
_f2g : focal length of the second lens group f: focal length of the optical system when focused at infinity

Equation (7) represents an equation in which the focal length of the second lens group is normalized by the focal length of the optical system when focused at infinity. Satisfying equation (7) is preferable from the viewpoint of ensuring a sufficient back focus (BF) and realizing a shortened overall optical length of the optical system. If the lower limit of equation (7) is not satisfied, it may not be possible to ensure a sufficient back focus. Furthermore, if the upper limit of equation (7) is exceeded, the positive refractive power of the second lens group may become too small, making it difficult to realize a shortened overall optical length of the optical system.

From the viewpoint of ensuring a sufficient back focus, f _2g /f is more preferably greater than 1.40, and even more preferably greater than 1.50. Also, from the viewpoint of realizing a reduction in the total optical length of the optical system, f _2g /f is more preferably less than 2.60, and even more preferably less than 2.55.

It is preferable that the optical system according to this embodiment satisfies the following formula.
5.0<oal/f<8.0 (8)
however,
oal: total optical length of the optical system f: focal length of the optical system when focused at infinity

Equation (8) represents an equation in which the total optical length of the optical system is normalized by the focal length of the optical system when focused at infinity. In this embodiment, the total optical length of the optical system is the distance on the optical axis from the object-side surface of the first lens L1 in the optical system to the image plane. Satisfying equation (8) is preferable from the viewpoint of ensuring a sufficient back focus and realizing a shortened total optical length of the optical system. If the lower limit of equation (8) is not satisfied, it may not be possible to ensure a sufficient back focus. Furthermore, if the upper limit of equation (8) is exceeded, it may be difficult to realize a shortened total optical length of the optical system.

From the viewpoint of ensuring a sufficient back focus, oal/f is preferably greater than 5.5, and more preferably greater than 5.8. Furthermore, from the viewpoint of realizing a reduction in the total optical length of the optical system, oal/f is preferably less than 7.0, and more preferably less than 6.7.

It is preferable that the optical system according to this embodiment satisfies the following formula.
-2.40<f _1g /f<-0.75 (9)
however,
_f1g : focal length of the first lens group f: focal length of the optical system when focused at infinity

Equation (9) represents an equation in which the focal length of the first lens group is normalized by the focal length of the optical system when focused at infinity. Satisfying equation (9) is preferable from the viewpoint of ensuring a sufficient back focus and shortening the overall optical length of the optical system. If the lower limit of equation (9) is not satisfied, it may not be possible to ensure a sufficient back focus. Furthermore, if the upper limit of equation (9) is exceeded, the absolute value of the negative refractive power of the first lens group becomes too large, making it difficult to shorten the overall optical length of the optical system.

From the viewpoint of ensuring a sufficient back focus, f _1g /f is more preferably greater than −2.35, and from the viewpoint of realizing a reduction in the total optical length of the optical system, f _1g /f is more preferably less than −0.80, and even more preferably less than −0.85.

It is preferable that the optical system according to this embodiment satisfies the following formula.
0.50<R _L1r /f<10.00 (10)
however,
R _L1r : Radius of curvature of the lens surface on the image side of the first lens L1 f: Focal length of the optical system when focused at infinity

Equation (10) represents an equation in which the radius of curvature of the lens surface on the image side of the first lens L1 is normalized by the focal length when the optical system is focused at infinity. Satisfying equation (10) is preferable from the viewpoint of obtaining distortion that satisfies an appropriate projection method and realizing a shortened overall optical length of the optical system. If the lower limit of equation (10) is not met, it may be difficult to obtain distortion that satisfies an appropriate projection method and to realize a shortened overall optical length of the optical system. Furthermore, if the upper limit of equation (10) is exceeded, the positive refractive power of the lens surface on the image side of the first lens L1 becomes too large, and it may be difficult to realize a shortened overall optical length of the optical system.

From the viewpoints of obtaining distortion that satisfies an appropriate projection method and realizing a reduction in the overall optical length of the optical system, R _L1r /f is more preferably greater than 0.53, and even more preferably greater than 0.55. Also, from the viewpoints of realizing a reduction in the overall optical length of the optical system, R _L1r /f is more preferably less than 2.00, and even more preferably less than 1.50.

It is preferable that the optical system according to this embodiment satisfies the following formula.
1.70<N _L1 <2.00 (11)
however,
N _L1 : the refractive index at the d line of the first lens L1

Equation (11) represents the refractive index at the d-line of the first lens L1. Satisfying equation (11) means that the glass has a higher refractive index relative to the first lens L1, which has a negative refractive power. Satisfying equation (11) is preferable from the viewpoint of appropriately correcting the Petzval sum and appropriately correcting distortion or coma. If the lower limit of equation (11) is not satisfied, it may be difficult to appropriately correct the Petzval sum. Also, if the upper limit of equation (11) is exceeded, it may be difficult to appropriately correct distortion or coma.

From the viewpoint of appropriately correcting the Petzval sum, N _L1 is more preferably greater than 1.72, and even more preferably greater than _1.74 , and more preferably less than 1.95, and even more preferably less than 1.92.

It is preferable that the optical system according to this embodiment satisfies the following formula.
1.60<N _L3 <2.00 (12)
N _L3 : The refractive index of the third lens L3 at the d line

Expression (12) represents the refractive index at the d-line of the third lens L3. Satisfying expression (12) means that the third lens L3 has positive refractive power and is a relatively high refractive index glass. Satisfying expression (12) is preferable from the viewpoint of appropriately correcting coma aberration occurring in the first lens group having negative refractive power. If the lower limit of expression (12) is not satisfied, it may be difficult to appropriately correct coma aberration occurring in the first lens group having negative refractive power. If the upper limit of expression (12) is exceeded, coma aberration occurring in the first lens group having negative refractive power may be over-corrected.

From the viewpoint of appropriately correcting coma occurring in the first lens group having negative refractive power, N _L3 is more preferably greater than 1.62, even more preferably greater than 1.64, and particularly preferably greater than 1.70. Also, from the viewpoint of preventing overcorrection of coma occurring in the first lens group having negative refractive power, N _L3 is more preferably less than 1.96, even more preferably less than 1.94, and particularly preferably less than 1.93.

It is preferable that the optical system according to this embodiment satisfies the following formula.
0.01<D _L23 /f<0.05 (13)
however,
D _L23 : The distance on the optical axis between the lens surface on the image side of the second lens L2 and the lens surface on the object side of the third lens L3 when the optical system is focused on infinity. f: The focal length of the optical system when focused on infinity.

Formula (13) represents the axial distance between the lens surface on the image side of the second lens L2 and the lens surface on the object side of the third lens L3 when the optical system is focused at infinity, normalized by the focal length when the optical system is focused at infinity. Satisfying formula (13) is preferable from the viewpoint of maintaining a distance that does not collide during lens assembly and converging the light beam diameter that has spread too much in the first lens group at the third lens L3 on the image side adjacent to the second lens L2 arranged at a close distance to properly correct aberration. If the lower limit of formula (13) is not met, it may not be possible to maintain a distance that does not collide during lens assembly. Also, if the upper limit of formula (13) is exceeded, it may not be possible to converge the light beam diameter that has spread too much in the first lens group at the third lens L3 on the image side adjacent to the second lens L2 arranged at a close distance to properly correct aberration.

From the viewpoint of maintaining a collision-free distance during lens assembly, D _L23 /f is more preferably greater than 0.013, and even more preferably greater than 0.015. Also, from the viewpoint of appropriately correcting aberration by converging a light beam diameter that has spread too much in the first lens group by the third lens L3 on the image side adjacent to the closely arranged second lens L2, D _L23 /f is more preferably less than 0.030, and even more preferably less than 0.025.

It is preferable that the optical system according to this embodiment satisfies the following formula.
1.5<f _Lf /f<4.5 (14)
however,
f _Lf : focal length of the final lens Lf f: focal length of the optical system when focused at infinity

Equation (14) represents an equation in which the focal length of the final lens Lf, which is the lens in the second lens group closest to the image surface, is normalized by the focal length of the optical system when focused at infinity. Satisfying equation (14) is preferable from the viewpoints of preventing the incidence angle of the sensor from becoming large, maintaining the amount of peripheral light appropriately, and realizing a reduction in the length of the lens barrel and the overall optical length of the optical system. If the lower limit of equation (14) is not met, the incidence angle of the sensor becomes too large, making it difficult to maintain the amount of peripheral light appropriately. Furthermore, if the upper limit of equation (14) is exceeded, the back focus cannot be increased, making it difficult to realize a reduction in the length of the lens barrel and the overall optical length of the optical system.

From the viewpoint of preventing the incident angle of the sensor from becoming large and maintaining an appropriate amount of peripheral light, f _Lf /f is more preferably greater than 1.9, and even more preferably greater than 2.1. Also, from the viewpoint of realizing a reduction in the length of the lens barrel and the total optical length of the optical system, f _Lf /f is more preferably less than 4.0, and even more preferably less than 3.7.

2. Imaging Device Next, an imaging device according to an embodiment of the present invention will be described. The imaging device includes an optical system according to the above embodiment, and an imaging element provided on the image plane side of the optical system, which converts an optical image formed by the optical system into an electrical signal. The optical system in this embodiment is, for example, a fixed focal length lens.

Here, the imaging element is not limited, and solid-state imaging elements such as CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors, silver halide film, infrared cut filters (IRCF), etc. can also be used. The imaging device according to this embodiment is suitable for imaging devices using the above-mentioned solid-state imaging elements, such as FA cameras, digital cameras, and video cameras. In addition, the imaging device may be a fixed-lens imaging device in which the lens is fixed to the housing, or a lens-interchangeable imaging device such as a single-lens reflex camera or a mirrorless single-lens camera.

Fig. 19 is a diagram showing a schematic example of the configuration of an imaging device according to this embodiment. As shown in Fig. 19, a mirrorless single-lens camera 1 has a body 2 and a lens barrel 3 that is detachable from the body 2. The mirrorless single-lens camera 1 is one form of an imaging device.

The lens barrel 3 has an optical system 30. The optical system 30 includes a first lens group 31 and a second lens group 32, and is configured to satisfy, for example, the above-mentioned expressions (1) and (2). In addition, an aperture 33 is disposed in the second lens group 32.

The first lens group 31 consists of, from the object side, a first lens L1 that has a convex surface facing the object side and negative refractive power, and a second lens L2 that has a meniscus shape and a concave surface facing the object side, and the second lens group 32 has positive refractive power.

The main body 2 has a CCD sensor 21 as an image sensor and an infrared cut filter 22. The CCD sensor 21 is disposed in the main body 2 at a position where the optical axis OA of the optical system 30 in the lens barrel 3 attached to the main body 2 is the central axis. Instead of the infrared cut filter 22, the main body 2 may have a parallel plate that does not have substantial refractive power, such as a cover glass.

The imaging device according to this embodiment preferably includes an image processing unit that electrically processes the captured image data acquired by the imaging element to change the shape of the captured image, and an image correction data storage unit that stores image correction data and an image correction program used to process the captured image data in the image processing unit, for example to enlarge (zoom) a key part of the image.

When the optical system is made smaller, distortion (curvature) of the captured image shape formed on the imaging surface is more likely to occur. In such cases, it is preferable to correct the distortion of the captured image shape. This correction can be performed, for example, by storing distortion correction data for correcting the distortion of the captured image shape in advance in the image correction data storage unit, and using the distortion correction data stored in the image correction data storage unit in the image processing unit. With such an imaging device, it is possible to further miniaturize the optical system, obtain a beautiful captured image, and miniaturize the entire imaging device.

Furthermore, in the imaging device according to this embodiment, it is preferable that the image correction data storage unit stores magnification chromatic aberration correction data in advance. It is also preferable that the image processing unit performs magnification chromatic aberration correction of the captured image using the magnification chromatic aberration correction data stored in the image correction data storage unit. By correcting the magnification chromatic aberration, i.e., color distortion aberration, with the image processing unit, it is possible to reduce the number of lenses that make up the optical system. Therefore, with such an imaging device, it is possible to further miniaturize the optical system.

The optical system according to this embodiment can be configured as a small optical system, and can capture images with a wide angle and maintain high resolution from the center of the image to the periphery of the image. For this reason, the optical system according to this embodiment is suitable for use as an optical system for digital input/output devices such as vehicle-mounted lenses using solid-state imaging elements and drone single-focus lenses. Since the imaging device according to this embodiment is equipped with this optical system, it can be suitable for use as an imaging device for vehicles or drones by providing a zoom function using image processing as necessary. Such an imaging device according to this embodiment can achieve the imaging functions required for an in-vehicle camera that can be applied to level 3 autonomous driving in automobiles.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in the different embodiments are also included in the technical scope of the present invention.

One embodiment of the present invention is described below.

An embodiment of the present invention will be described below. In the following tables, all lengths are in mm, and all angles of view are in degrees. Furthermore, "E-a" indicates "×10 ^-a ."

[Example 1]
FIG. 1 is a diagram showing a schematic optical configuration of the optical system of Example 1 when focusing at infinity. The optical system of Example 1 is composed of, in order from the object side, a first lens L1 having a negative refractive power, a second lens L2 having a negative refractive power, a third lens L3 having a positive refractive power, a diaphragm S, a fourth lens L4 having a positive refractive power, a fifth lens L5 having a negative refractive power, and a sixth lens L6 having a positive refractive power. The sixth lens L6 corresponds to the above-mentioned final lens Lf. "IMG" shown in FIG. 1 is an image plane (image forming plane), and an infrared cut filter IRCF is arranged between the sixth lens L6 and the image plane IMG.

The configuration of each lens group will be described below. The first lens group is composed of, from the object side, a first lens L1 which is a negative meniscus lens with a convex shape toward the object side, and a second lens L2 which is a negative meniscus lens with a concave shape toward the object side. The second lens group is composed of, from the object side, a third lens L3 which is a biconvex lens, an aperture stop S, a fourth lens L4 which is a biconvex lens, a fifth lens L5 which is a biconcave lens, and a sixth lens L6 which is a biconvex lens. The fourth lens L4 and the fifth lens L5 are cemented together.

Next, we will explain an example in which specific numerical values of the optical system are applied. Table 1 shows the surface data of the optical system in Example 1.

In the table of surface data for the embodiments of the present invention, "Surface No." indicates the order of the lens surface counted from the object side, "r" indicates the radius of curvature of the lens surface, "d" indicates the distance on the optical axis of the lens surfaces, "Nd" indicates the refractive index for the d-line (wavelength λ=587.56 nm), and "vd" indicates the Abbe number for the d-line. In the surface number, "S" indicates that it is an aperture, and "*" indicates that the lens surface is aspheric.

In addition, "INF" in the radius of curvature means a plane. In Table 1, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 14 are the surface numbers of the second lens group, and No. 8 represents the aperture. Nos. 15 and 16 represent the infrared cut filter IRCF.

[Table 1]
Surface No. rd Nd vd
1. INF
2* 8.407 1.500 1.8820 37.20
3* 3.641 6.898
4* -6.240 3.784 1.8513 40.10
5* -9.136 0.100
6* 9.267 3.921 1.7730 49.50
7* -77.737 4.088
8S 0.000 0.390
9 14.790 2.958 1.6180 63.40
10 -5.250 0.000
11 -5.250 0.900 1.8052 25.46
12 38.433 2.936
13* 7.794 3.187 1.5920 67.02
14* -100.000 0.500
15 0.000 0.500 1.5163 64.14
16 0.000 3.324

Table 2 shows the specifications of the optical system of Example 1. In this specification table, "f" is the focal length of the optical system when focused at infinity, "Fno." is the F-number, "OBJ" is the object distance, "ω" is the half angle of view, "Cra" is the chief ray incidence angle, and "Y" is the effective image height.

[Table 2]
f 5.331
Fno 1.850
OBJ INF
ω 54.9
Cra 9.2
Y 5.17

Table 3 shows the aspheric coefficients of each aspheric surface in the optical system of Example 1. The aspheric coefficients in this table are values when each aspheric surface shape is defined by the following formula.

^{[ Formula ] ​ ​ ​ ​ ​}

In the above formula, "X" is the amount of displacement from the reference surface in the optical axis direction, "C" is the curvature at the vertex of the surface, "Y" is the height from the optical axis in a direction perpendicular to the optical axis, "K" is the Conic coefficient, and "An" is the n-th order aspheric coefficient.

[Table 3]
Surface No. k A4 A6
2 0.000000 -6.661500E-04 4.611810E-06
3 0.346700 -6.387730E-04 -1.037660E-05
4 0.483500 7.346440E-04 -2.175150E-05
5 0.647200 2.211580E-04 -4.890540E-06
6 0.322400 -5.481460E-05 2.635330E-06
7 -8.900000 -8.899630E-05 8.167050E-06
13 0.787300 -4.265000E-04 1.084120E-05
14 -9.000000 -1.653140E-04 1.851110E-05
Surface No. A8 A10
2 -3.495280E-08 2.962550E-10
3 -1.071340E-07 -1.877370E-08
4 2.498880E-07 -5.519630E-09
5 3.467870E-08 -8.426310E-11
6 1.646760E-08 -4.373810E-10
7 -1.585050E-07 1.135030E-09
13 -3.107950E-07 3.922260E-09
14 -6.186870E-07 8.579220E-09

Table 4 shows the focal length of each lens that constitutes the optical system of Example 1.

[Table 4]
Lens No. Focal length
1 -8.542
2 -57.957
3 10.926
4 6.644
5 -5.684
6 12.349

Figure 2 shows the longitudinal aberration of the optical system of Example 1 when focused at infinity. The longitudinal aberrations shown in each figure are, from the left as you face the figure, spherical aberration (mm), astigmatism (mm), and distortion (%), respectively.

In the graph showing spherical aberration, the vertical axis shows the ratio to the maximum aperture F-number, and the horizontal axis shows defocus. In the graph showing spherical aberration, the solid line shows spherical aberration at the d-line (wavelength λ = 587.6 nm), the dashed line shows spherical aberration at the g-line (wavelength λ = 435.8 nm), and the dotted line shows spherical aberration at the C-line (wavelength λ = 656.3 nm).

In the diagrams showing astigmatism, the vertical axis represents the angle of incidence and the horizontal axis represents defocus. Note that "Angle" in the aberration diagrams represents the angle of view. In the diagrams showing astigmatism, the solid line represents the sagittal image plane (S) for the d-line, and the four-dot chain line represents the meridional image plane (T) for the d-line.

In the diagrams showing distortion aberration, the vertical axis represents the angle of incidence, and the horizontal axis represents the percentage. Note that "Angle" in the aberration diagram represents the angle of view. The matters relating to these longitudinal aberration diagrams are the same in the longitudinal aberration diagrams shown in the other examples, so a description thereof will be omitted below.

[Example 2]
The optical configuration of the optical system of Example 2 when focusing at infinity is shown in Fig. 3, and the longitudinal aberration of the optical system of Example 2 when focusing at infinity is shown in Fig. 4. The optical system of Example 2 is composed of, in order from the object side, a first lens L1 having negative refractive power, a second lens L2 having negative refractive power, a third lens L3 having positive refractive power, a diaphragm S, a fourth lens L4 having positive refractive power, a fifth lens L5 having negative refractive power, and a sixth lens L6 having positive refractive power. The sixth lens L6 corresponds to the above-mentioned final lens Lf. An infrared cut filter IRCF is arranged between the sixth lens L6 and the image surface IMG.

The configuration of each lens group will be described below. The first lens group is composed of, from the object side, a first lens L1 which is a negative meniscus lens with a convex shape toward the object side, and a second lens L2 which is a negative meniscus lens with a concave shape toward the object side. The second lens group is composed of, from the object side, a third lens L3 which is a positive meniscus lens with a convex shape toward the object side, a diaphragm S, a fourth lens L4 which is a biconvex lens, a fifth lens L5 which is a negative meniscus lens with a convex shape toward the image side, and a sixth lens L6 which is a biconvex lens. The fourth lens L4 and the fifth lens L5 are cemented together.

Table 5 shows the surface data of the optical system of Example 2. In Table 5, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 14 are the surface numbers of the second lens group, and No. 8 represents the aperture. Nos. 15 and 16 represent the infrared cut filters IRCF.

[Table 5]
Surface No. rd Nd vd
1 INF INF
2* 9.221 1.500 1.8820 37.22
3* 3.863 7.110
4* -6.154 3.904 1.8820 37.22
5* -9.149 0.100
6* 8.127 4.031 1.8513 40.10
7* 86.305 3.477
8S 0.000 0.100
9 19.863 3.195 1.5935 67.00
10 -4.581 0.000
11 -4.581 0.900 1.8697 20.02
12 -130.673 2.914
13* 8.755 3.630 1.6889 31.16
14* -100.000 0.500
15 0.000 0.500 1.5163 64.14
16 0.000 3.139

Table 6 shows the specifications of the optical system of Example 2. Table 7 shows the aspheric coefficients of each aspheric surface in the optical system of Example 2. Table 8 shows the focal length of each lens that constitutes the optical system of Example 2.

[Table 6]
f 5.332
Fno 1.850
OBJ INF
ω 54.9
Cra 9.3
Y 5.17

[Table 7]
Surface No. k A4 A6
2 0.110100 -5.679470E-04 4.108850E-06
3 0.362500 -4.616820E-04 -1.076100E-05
4 0.540800 7.235910E-04 -1.735300E-05
5 0.665300 2.137450E-04 -4.615580E-06
6 0.522800 1.184160E-05 1.874130E-06
7 -9.000000 2.982540E-05 8.564620E-06
13 1.223500 -3.830780E-04 7.440420E-06
14 -2500.000 -1.399210E-04 1.598730E-05
Surface No. A8 A10
2 -3.401790E-08 2.477320E-10
3 1.389640E-07 -1.729760E-08
4 1.513600E-07 -4.140330E-09
5 2.232200E-08 -4.656680E-12
6 2.891490E-08 -4.527540E-12
7 -1.797910E-07 1.266680E-09
13 -2.323520E-07 3.288970E-09
14 -5.587700E-07 9.439520E-09

[Table 8]
Lens No. Focal length
1 -8.675
2 -54.808
3 10.294
4 6.593
5 -5.477
6 11.846

[Example 3]
The optical configuration of the optical system of Example 3 when focused at infinity is shown in Fig. 5, and the longitudinal aberration of the optical system of Example 3 when focused at infinity is shown in Fig. 6. The optical system of Example 3 is composed of, in order from the object side, a first lens L1 having negative refractive power, a second lens L2 having negative refractive power, a third lens L3 having positive refractive power, a stop S, a fourth lens L4 having positive refractive power, and a fifth lens L5 having negative refractive power. The fifth lens L5 corresponds to the above-mentioned final lens Lf. An infrared cut filter IRCF is arranged between the fifth lens L5 and the image surface IMG.

The configuration of each lens group is explained below. The first lens group is composed of, from the object side, a first lens L1 which is a negative meniscus lens with a convex shape toward the object side, and a second lens L2 which is a negative meniscus lens with a concave shape toward the object side. The second lens group is composed of, from the object side, a third lens L3 which is a biconvex lens, a stop, a fourth lens L4 which is a biconvex lens, and a fifth lens L5 which is a negative meniscus lens with a concave shape toward the object side. The fourth lens L4 and the fifth lens L5 are cemented together.

Table 9 shows the surface data of the optical system of Example 3. In Table 9, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 12 are the surface numbers of the second lens group, and No. 8 represents the aperture. Nos. 13 and 14 represent the infrared cut filters IRCF.

[Table 9]
Surface No. rd Nd vd
1 INF INF
2* 10.197 1.500 1.7725 49.62
3* 3.670 3.996
4* -8.083 5.449 1.9044 26.80
5* -14.518 0.100
6* 20.070 4.000 1.4970 81.61
7* -6.697 0.100
8S 0.000 8.009
9 12.018 5.000 1.6168 63.48
10 -7.500 0.000
11 -7.500 0.900 1.9229 20.88
12* -21.667 2.109
13 0.000 0.500 1.5163 64.14
14 0.000 3.337

Table 10 shows the specifications of the optical system of Example 3. Table 11 shows the aspheric coefficients of each aspheric surface in the optical system of Example 3. Table 12 shows the focal length of each lens that constitutes the optical system of Example 3.

[Table 10]
f 5.485
Fno 1.990
OBJ INF
ω 54.9
Cra 10.2
Y 5.21

[Table 11]
Surface No. k A4 A6
2 2.000000 -1.074770E-03 2.622180E-05
3 0.813100 -1.797520E-03 -5.902920E-05
4 3.983300 -1.706300E-04 1.078940E-05
5 5.965300 3.458580E-04 4.963130E-06
6 1.991700 2.050880E-06 -1.963500E-05
7 0.804200 1.003330E-04 -8.712480E-06
12 2.286100 1.441920E-04 -3.753840E-06
Surface No. A8 A10
2 -3.577230E-07 1.853520E-09
3 4.245290E-06 -2.356850E-07
4 7.521900E-07 8.200190E-08
5 1.178080E-06 -5.320810E-10
6 2.001380E-06 -3.238090E-08
7 2.340480E-07 5.136970E-09
12 3.515790E-08 -3.170560E-10

[Table 12]
Lens No. Focal length
1 -8.248
2 -33.720
3 10.631
4 8.299
5 -12.820

[Example 4]
The optical configuration of the optical system of Example 4 when focusing at infinity is shown in Fig. 7, and the longitudinal aberration of the optical system of Example 4 when focusing at infinity is shown in Fig. 8. The optical system of Example 4 is composed of, in order from the object side, a first lens L1 having negative refractive power, a second lens L2 having negative refractive power, a third lens L3 having positive refractive power, a stop S, a fourth lens L4 having positive refractive power, a fifth lens L5 having negative refractive power, and a sixth lens L6 having positive refractive power. The sixth lens L6 corresponds to the above-mentioned final lens Lf. An infrared cut filter IRCF is arranged between the sixth lens L6 and the image surface IMG.

The configuration of each lens group will be described below. The first lens group is composed of, from the object side, a first lens L1 which is a negative meniscus lens with a convex shape toward the object side, and a second lens L2 which is a negative meniscus lens with a concave shape toward the object side. The second lens group is composed of, from the object side, a third lens L3 which is a biconvex lens, an aperture stop S, a fourth lens L4 which is a biconvex lens, a fifth lens L5 which is a biconcave lens, and a sixth lens L6 which is a biconvex lens. The fourth lens L4 and the fifth lens L5 are cemented together.

Table 13 shows the surface data of the optical system of Example 4. In Table 13, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 14 are the surface numbers of the second lens group, and No. 8 represents the aperture. Nos. 15 and 16 represent the infrared cut filters IRCF.

[Table 13]
Surface No. rd Nd vd
1 INF INF
2* 12.516 1.500 1.8820 37.20
3* 3.993 5.162
4* -15.729 5.934 1.8513 40.10
5* -79.099 0.100
6* 10.419 3.480 1.8881 36.18
7* -32.897 1.870
8S 0.000 0.363
9 10.906 4.495 1.6180 63.40
10 -6.000 0.000
11 -6.000 0.600 1.8080 23.82
12 20.851 1.851
13* 13.812 2.416 1.5920 67.02
14* -18.144 4.500
15 0.000 0.500 1.5163 64.14
16 0.000 2.229

Table 14 shows the specifications of the optical system of Example 4. Table 15 shows the aspheric coefficients of each aspheric surface in the optical system of Example 4. Table 16 shows the focal length of each lens that constitutes the optical system of Example 4.

[Table 14]
f 5.421
Fno 1.850
OBJ INF
ω 54.9
Cra 15.6
Y 4.95

[Table 15]
Surface No. k A4 A6
2 0.000000 -6.617760E-04 5.035400E-06
3 0.492500 -3.521840E-04 -1.170940E-05
4 0.000000 5.299370E-04 -9.644310E-06
5 0.000000 1.313200E-04 -5.666370E-06
6 0.452500 -3.353340E-05 1.257310E-06
7 -9.000000 1.787490E-05 6.345430E-06
13 0.000000 -8.748250E-04 -5.621190E-06
14 2.000000 -2.139510E-04 -1.255270E-05
Surface No. A8 A10
2 -9.720780E-09 -2.838990E-11
3 3.544680E-07 -3.215530E-08
4 1.534870E-07 -3.567140E-09
5 -2.925960E-08 4.380300E-10
6 -1.258370E-08 -5.600150E-10
7 -1.550270E-07 8.389010E-10
13 -8.742540E-07 0.000000
14 -3.790750E-07 0.000000

[Table 16]
Lens No. Focal length
1 -7.247
2 -24.099
3 9.260
4 6.971
5 -5.709
6 13.630

[Example 5]
The optical configuration of the optical system of Example 5 when focusing at infinity is shown in Fig. 9, and the longitudinal aberration of the optical system of Example 5 when focusing at infinity is shown in Fig. 10. The optical system of Example 5 is composed of, in order from the object side, a first lens L1 having negative refractive power, a second lens L2 having negative refractive power, a third lens L3 having positive refractive power, a diaphragm S, a fourth lens L4 having positive refractive power, a fifth lens L5 having negative refractive power, and a sixth lens L6 having positive refractive power. The sixth lens L6 corresponds to the above-mentioned final lens Lf. An infrared cut filter IRCF is arranged between the sixth lens L6 and the image surface IMG.

The configuration of each lens group will be described below. The first lens group is composed of, from the object side, a first lens L1 which is a negative meniscus lens with a convex shape toward the object side, and a second lens L2 which is a negative meniscus lens with a concave shape toward the object side. The second lens group is composed of, from the object side, a third lens L3 which is a biconvex lens, a diaphragm S, a fourth lens L4 which is a biconvex lens, a fifth lens L5 which is a concave lens toward the object side, and a sixth lens L6 which is a convex-planar lens. The fourth lens L4 and the fifth lens L5 are cemented together.

Table 17 shows the surface data of the optical system of Example 5. In Table 17, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 14 are the surface numbers of the second lens group, and No. 8 represents the aperture. Nos. 15 and 16 represent the infrared cut filters IRCF.

[Table 17]
Surface No. rd Nd vd
1 INF INF
2* 58.490 1.500 1.7680 49.24
3* 5.457 7.151
4* -4.783 2.500 1.9520 29.80
5* -6.878 0.100
6* 9.005 4.388 1.7725 49.62
7* -53.449 5.232
8S 0.000 0.100
9 22.503 3.471 1.5930 67.00
10 -5.000 0.000
11 -5.000 0.600 2.0027 19.32
12 -15.268 4.620
13 14.901 2.300 1.9212 23.96
14 0.000 0.500
15 0.000 0.500 1.5163 64.14
16 0.000 3.075

Table 18 shows the specifications of the optical system of Example 5. Table 19 shows the aspheric coefficients of each aspheric surface in the optical system of Example 5. Table 20 shows the focal length of each lens that constitutes the optical system of Example 5.

[Table 18]
f 5.435
Fno 1.850
OBJ INF
ω 54.9
Cra 15.6
Y 4.95

[Table 19]
Surface No. k A4 A6
2 2.000000 -1.104330E-04 3.008990E-06
3 0.712500 -2.709220E-04 -8.866030E-06
4 0.395100 2.492690E-04 -1.036640E-05
5 0.505800 1.430470E-04 -9.440480E-07
6 0.358400 -4.603160E-05 2.662070E-06
7 0.526700 -4.854810E-06 5.065450E-06
Surface No. A8 A10
2 -3.230510E-08 1.758280E-10
3 2.763750E-07 -8.659980E-09
4 2.857530E-07 0.000000
5 5.128250E-08 0.000000
6 -2.043410E-08 1.578400E-10
7 -7.193020E-08 3.771070E-10

[Table 20]
Lens No. Focal length
1 -7.934
2 -39.455
3 10.291
4 7.239
5 -7.638
6 16.176

[Example 6]
The optical configuration of the optical system of Example 6 when focusing at infinity is shown in Fig. 11, and the longitudinal aberration of the optical system of Example 6 when focusing at infinity is shown in Fig. 12. The optical system of Example 6 is composed of, in order from the object side, a first lens L1 having negative refractive power, a second lens L2 having negative refractive power, a third lens L3 having positive refractive power, a fourth lens L4 having positive refractive power, a stop S, a fifth lens L5 having positive refractive power, a sixth lens L6 having negative refractive power, and a seventh lens L7 having positive refractive power. The seventh lens L7 corresponds to the above-mentioned final lens Lf. An infrared cut filter IRCF is arranged between the seventh lens L7 and the image surface IMG.

The configuration of each lens group will be described below. The first lens group is composed of, from the object side, a first lens L1 which is a negative meniscus lens with a convex shape toward the object side, and a second lens L2 which is a negative meniscus lens with a concave shape toward the object side. The second lens group is composed of, from the object side, a third lens L3 which is a positive meniscus lens with a convex shape toward the object side, a fourth lens L4 which is a positive meniscus lens with a convex shape toward the object side, an aperture stop S, a fifth lens L5 which is a biconvex lens, a sixth lens L6 which is a meniscus lens with a concave shape toward the object side, and a seventh lens L7 which is a biconvex lens. The fifth lens L5 and the sixth lens L6 are cemented together.

Table 21 shows the surface data of the optical system of Example 6. In Table 21, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 16 are the surface numbers of the second lens group, and No. 10 represents the aperture. Nos. 17 and 18 represent the infrared cut filters IRCF.

[Table 21]
Surface No. rd Nd vd
1 INF INF
2* 34.312 1.500 1.8820 37.20
3* 6.132 4.781
4* -5.975 4.873 1.7543 50.69
5* -8.332 0.100
6* 8.297 3.102 1.6663 36.49
7* 12.102 1.300
8 13.809 1.593 1.6180 63.40
9 107.260 2.244
10S 0.000 0.100
11 11.022 4.813 1.5319 74.44
12 -6.000 0.000
13 -6.000 0.600 1.8951 21.46
14 -30.682 1.868
15 21.475 1.926 1.8830 40.81
16 -74.424 4.500
17* 0.000 0.500 1.5163 64.14
18* 0.000 1.200

Table 22 shows the specifications of the optical system of Example 6. Table 23 shows the aspheric coefficients of each aspheric surface in the optical system of Example 6. Table 24 shows the focal length of each lens that constitutes the optical system of Example 6.

[Table 22]
f 5.559
Fno 1.850
OBJ INF
ω 54.9
Cra 15.6
Y 4.95

[Table 23]
Surface No. k A4 A6
2 0.000000 5.137190E-05 2.139890E-06
3 1.135900 1.637820E-04 1.027120E-06
7 0.967600 7.942720E-04 1.116260E-05
8 0.661500 3.597830E-04 -1.722780E-06
9 0.606100 -9.246350E-05 2.593290E-06
10 -6.572800 -4.845440E-05 9.418390E-06
11 0.000000 -9.576370E-04 -5.468110E-06
12 2.000000 -8.200080E-04 -4.905930E-06
Surface No. A8 A10
2 -7.954220E-08 6.188000E-10
3 7.892610E-07 -1.496300E-08
7 1.453470E-08 3.924980E-09
8 4.289570E-08 -1.089900E-09
9 -9.998790E-09 -4.200260E-10
10 -1.665500E-07 6.349930E-10
11 -4.896800E-07 0.000000
12 -2.107430E-07 0.000000

[Table 24]
Lens No. Focal length
1 -8.683
2 -252.705
3 29.862
4 25.481
5 8.099
6 -8.430
7 19.054

[Example 7]
The optical configuration of the optical system of Example 7 when focusing at infinity is shown in Fig. 13, and the longitudinal aberration of the optical system of Example 7 when focusing at infinity is shown in Fig. 14. The optical system of Example 7 is composed of, in order from the object side, a first lens L1 having negative refractive power, a second lens L2 having negative refractive power, a third lens L3 having negative refractive power, a fourth lens L4 having positive refractive power, a fifth lens L5 having negative refractive power, a diaphragm S, a sixth lens L6 having positive refractive power, a seventh lens L7 having negative refractive power, and an eighth lens L8 having positive refractive power. The eighth lens L8 corresponds to the above-mentioned final lens Lf. An infrared cut filter IRCF is arranged between the eighth lens L8 and the image surface IMG.

The configuration of each lens group will be described below. The first lens group is composed of, from the object side, a first lens L1 which is a negative meniscus lens convex toward the object side, and a second lens L2 which is a negative meniscus lens concave toward the object side. The second lens group is composed of, from the object side, a third lens L3 which is a negative meniscus lens convex toward the object side, a fourth lens L4 which is a biconvex positive lens, a fifth lens L5 which is a negative meniscus lens concave toward the image side, a diaphragm S, a sixth lens L6 which is a biconvex lens, a seventh lens L7 which is a negative meniscus lens concave toward the object side, and an eighth lens L8 which is a biconvex lens. The sixth lens L6 and the seventh lens L7 are cemented together.

Table 25 shows the surface data of the optical system of Example 7. In Table 25, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 18 are the surface numbers of the second lens group, and No. 12 represents the aperture. Nos. 19 and 20 represent the infrared cut filters IRCF.

[Table 25]
Surface No. rd Nd vd
1 INF INF
2* 16.504 1.500 1.8820 37.20
3* 5.200 4.973
4* -8.236 4.410 1.8873 28.67
5* -10.744 0.100
6 9.928 2.356 1.9229 20.88
7 8.105 1.300
8 10.695 2.729 1.8830 40.81
9 -25.106 2.123
10 18.892 0.600 1.8431 22.75
11 9.224 0.635
12S 0.000 0.767
13 107.483 2.819 1.6180 63.40
14 -5.000 0.000
15 -5.000 0.600 1.9194 21.76
16 -11.002 0.651
17 21.990 1.770 1.8830 40.81
18 -47.208 4.500
19 0.000 0.500 1.5163 64.14
20 0.000 2.667

Table 26 shows the specifications of the optical system of Example 7. Table 27 shows the aspheric coefficients of each aspheric surface in the optical system of Example 7. Table 28 shows the focal length of each lens that constitutes the optical system of Example 7.

[Table 26]
f 5.599
Fno 1.850
OBJ INF
ω 54.9
Cra 19.3
Y 4.99

[Table 27]
Surface No. k A4 A6
2 1.286700 -1.303630E-04 -1.311580E-07
3 0.769500 4.850830E-05 -1.088170E-05
4 1.562300 2.767730E-04 8.137640E-06
5 1.128300 1.725830E-04 2.036530E-06
Surface No. A8 A10
2 -9.223720E-09 1.264010E-10
3 5.797910E-07 -2.243900E-08
4 -1.233300E-07 7.631740E-09
5 -4.689880E-09 1.114060E-09

[Table 28]
Lens No. Focal length
1 -9.179
2 -229.813
3 -125.971
4 8.809
5 -22.002
6 7.806
7 -10.469
8 17.196

[Example 8]
The optical configuration of the optical system of Example 8 when focusing at infinity is shown in Fig. 15, and the longitudinal aberration of the optical system of Example 8 when focusing at infinity is shown in Fig. 16. The optical system of Example 8 is composed of, in order from the object side, a first lens L1 having negative refractive power, a second lens L2 having negative refractive power, a third lens L3 having positive refractive power, a fourth lens L4 having positive refractive power, a fifth lens L5 having positive refractive power, a sixth lens L6 having negative refractive power, a diaphragm S, a seventh lens L7 having positive refractive power, an eighth lens L8 having negative refractive power, and a ninth lens L9 having positive refractive power. The ninth lens L9 corresponds to the above-mentioned final lens Lf. An infrared cut filter IRCF is arranged between the ninth lens L9 and the image surface IMG.

The configuration of each lens group will be described below. The first lens group is composed of, in order from the object side, the first lens L1, which is a negative meniscus lens with a convex shape toward the object side, and the second lens L2, which is a negative meniscus lens with a concave shape toward the object side. The second lens group is composed of, in order from the object side, the third lens L3, which is a positive meniscus lens with a convex shape toward the image side, the fourth lens L4, which is a positive lens with a biconvex shape, the fifth lens L5, which is a positive meniscus lens with a convex shape toward the object side, the sixth lens L6, which is a negative meniscus lens with a concave shape toward the image side, the aperture S, the seventh lens L7, which is a biconvex lens, the eighth lens L8, which is a negative meniscus lens with a concave shape toward the object side, and the ninth lens L9, which is a positive meniscus lens with a convex shape toward the object side. The seventh lens L7 and the eighth lens L8 are cemented together.

Table 29 shows the surface data of the optical system of Example 8. In Table 29, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 20 are the surface numbers of the second lens group, and No. 14 represents the aperture. Nos. 21 and 22 represent the infrared cut filters IRCF.

[Table 29]
Surface No. rd Nd vd
1 INF INF
2* 28.906 1.500 1.8820 37.20
3* 5.200 5.151
4 -8.438 3.671 1.4970 81.61
5 -11.671 0.100
6 -41.602 2.333 1.8830 40.81
7 -19.592 0.100
8 14.071 3.801 1.6666 57.57
9 -36.853 0.100
10 12.148 1.219 1.8830 40.81
11 21.659 2.743
12 20.487 0.600 1.8431 22.75
13 7.580 0.617
14S 0.000 0.333
15 16.881 3.099 1.5273 75.26
16 -5.250 0.000
17 -5.250 0.600 1.9195 21.73
18 -11.510 1.032
19 15.486 1.800 1.8830 40.81
20 178.611 4.500
21 0.000 0.500 1.5163 64.14
22 0.000 1.200

Table 30 shows the specifications of the optical system of Example 8. Table 31 shows the aspheric coefficients of each aspheric surface in the optical system of Example 8. Table 32 shows the focal length of each lens that constitutes the optical system of Example 8.

[Table 30]
f 5.493
Fno 1.850
OBJ INF
ω 54.9
Cra 11.3
Y 4.88

[Table 31]
Surface No. k A4 A6
2 1.980300 -3.558770E-04 6.743390E-06
3 0.673100 -1.651480E-04 -1.044690E-05
Surface No. A8 A10
2 -8.767810E-08 4.734460E-10
3 8.900840E-07 -2.475000E-08

[Table 32]
Lens No. Focal length
1 -7.409
2 -98.366
3 39.954
4 15.746
5 29.552
6 -14.582
7 7.980
8 -11.003
9 19.103

[Example 9]
The optical configuration of the optical system of Example 9 when focusing at infinity is shown in Fig. 17, and the longitudinal aberration of the optical system of Example 9 when focusing at infinity is shown in Fig. 18. The optical system of Example 9 is composed of, in order from the object side, a first lens L1 having negative refractive power, a second lens L2 having negative refractive power, a third lens L3 having positive refractive power, a fourth lens L4 having positive refractive power, a fifth lens L5 having positive refractive power, a sixth lens L6 having negative refractive power, a seventh lens L7 having positive refractive power, a diaphragm S, an eighth lens L8 having positive refractive power, a ninth lens L9 having negative refractive power, and a tenth lens having positive refractive power. The tenth lens L10 corresponds to the above-mentioned final lens Lf. An infrared cut filter IRCF is arranged between the tenth lens L10 and the image surface IMG.

The configuration of each lens group will be described below. The first lens group is composed of, in order from the object side, the first lens L1, which is a negative meniscus lens with a convex shape toward the object side, and the second lens L2, which is a negative meniscus lens with a concave shape toward the object side. The second lens group is composed of, in order from the object side, the third lens L3, which is a biconvex lens, the fourth lens L4, which is a positive meniscus lens with a convex shape toward the object side, the fifth lens L5, which is a biconvex lens, the sixth lens L6, which is a positive meniscus lens with a convex shape toward the object side, the seventh lens L7, which is a biconvex lens, the aperture S, the eighth lens L8, which is a biconvex lens, the ninth lens L9, which is a negative meniscus lens with a concave shape toward the object side, and the tenth lens L10, which is a biconvex lens. The eighth lens L8 and the ninth lens L9 are cemented together.

Table 33 shows the surface data of the optical system of Example 9. In Table 33, No. 1 is the surface number of the object surface. Nos. 2 to 5 are the surface numbers of the first lens group. Nos. 6 to 22 are the surface numbers of the second lens group, and No. 16 represents the aperture. Nos. 23 and 24 represent the infrared cut filters IRCF.

[Table 33]
Surface No. rd Nd vd
1 INF INF
2* 17.177 1.500 1.8820 37.20
3* 5.200 6.135
4 -6.158 3.984 1.8830 40.81
5 -9.169 0.100
6 287.123 2.528 1.8830 40.81
7 -23.655 0.100
8 9.081 2.726 1.9229 20.88
9 14.059 0.100
10 9.887 1.809 1.4970 81.61
11 -104.284 0.100
12 45.929 0.600 1.9229 20.88
13 6.894 0.415
14 10.140 1.174 1.4970 81.61
15 -470.253 0.100
16S 0.000 0.424
17 20.941 3.123 1.4970 81.61
18 -5.250 0.000
19 -5.250 0.600 1.9229 20.88
20 -14.841 1.483
21 26.076 1.800 1.9215 21.23
22 -48.190 4.500
23 0.000 0.500 1.5163 64.14
24 0.000 1.200

Table 34 shows the specifications of the optical system of Example 9. Table 35 shows the aspheric coefficients of each aspheric surface in the optical system of Example 9. Table 36 shows the focal length of each lens that constitutes the optical system of Example 9.

[Table 34]
f 5.604
Fno 1.850
OBJ INF
ω 54.9
Cra 19.9
Y 4.93

[Table 35]
Surface No. k A4 A6
2 1.070500 -4.629980E-04 1.296690E-05
3 1.080400 -6.080860E-04 -2.207820E-05
Surface No. A8 A10
2 -1.742400E-07 1.059700E-09
3 1.892430E-06 -5.997030E-08

[Table 36]
Lens No. Focal length
1 -8.983
2 -55.972
3 24.845
4 22.005
5 18.267
6 -8.855
7 19.988
8 8.794
9 -9.075
10 18.579

The values calculated using the above formulas in Examples 1 to 9 and the numerical values used in the formulas are shown in Table 37.

[Table 37]
Example 1 Example 2 Example 3 Example 4
Equation (1) (C _L1r -C _L2f )×f 2.318 2.247 2.173 1.702
Equation (2) D _L12 /f 1.294 1.334 0.728 0.952
Equation (3) f ₁₂ /f -1.506 -1.512 -1.286 -0.913
Equation (4) P _W12 ×f 2.019 1.982 1.768 1.491
Equation (5) f ₁ /f -1.602 -1.627 -1.504 -1.337
Equation (6) R _L2f /f -1.171 -1.154 -1.474 -2.902
Equation (7) f _2g /f 2.179 2.177 2.118 1.574
Equation (8) oal/f 6.565 6.564 6.381 6.456
Equation (9) f _1g /f -1.506 -1.512 -1.286 -0.913
Equation (10) R _L1r /f 0.683 0.724 0.669 0.737
Equation (11) N _L1 1.882 1.882 1.773 1.882
Equation (12) N _L3 1.773 1.851 1.497 1.888
Equation (13) D _L23 /f 0.018 0.019 0.018 0.018
Equation (14) f _Lf /f 2.316 2.222 -17.414 2.514
Example 1 Example 2 Example 3 Example 4
C _L1r 0.2746 0.2589 0.2725 0.2504
C _L2f -0.1602 -0.1625 -0.1237 -0.0636
f 5.331 5.332 5.485 5.421
D _L12 6.898 7.110 3.996 5.162
f ₁₂ -8.031 -8.063 -7.055 -4.952
P _W12 0.379 0.372 0.322 0.275
f ₁ -8.542 -8.675 -8.248 -7.247
R _L2f -6.240 -6.154 -8.083 -15.729
f _2g 11.615 11.615 11.615 8.533
oal 34.986 35.000 35.000 35.000
f _1g -8.031 -8.063 -7.054 -4.952
R _L1r 3.641 3.863 3.670 3.993
D _L23 0.100 0.100 0.100 0.100
f _Lf 12.349 11.846 -12.820 13.630
Example 5 Example 6 Example 7 Example 8 Example 9
Equation (1) (C _L1r -C _L2f )×f 2.132 1.837 1.765 1.707 1.988
Equation (2) D _L12 /f 1.316 0.860 0.888 0.938 1.095
Equation (3) f ₁₂ /f -1.214 -1.950 -1.891 -1.320 -1.512
Equation (4) P _W12 ×f 1.847 1.501 1.553 1.255 1.754
Equation (5) f ₁ /f -1.460 -1.562 -1.639 -1.349 -1.603
Equation (6) R _L2f /f -0.880 -1.075 -1.471 -1.536 -1.099
Equation (7) f _2g /f 2.487 2.031 1.917 1.829 1.809
Equation (8) oal/f 6.564 6.296 6.251 6.372 6.245
Equation (9) f _1g /f -1.203 -1.950 -1.951 -1.320 -1.512
Equation (10) R _L1r /f 1.004 1.103 0.929 0.947 0.928
Equation (11) N _L1 1.768 1.882 1.882 1.882 1.882
Equation (12) N _L3 1.773 1.666 1.923 1.883 1.883
Equation (13) D _L23 /f 0.018 0.018 0.018 0.018 0.018
Equation (14) f _Lf /f 2.976 3.427 3.072 3.478 3.315
Example 5 Example 6 Example 7 Example 8 Example 9
C _L1r 0.1833 0.1631 0.1923 0.1923 0.1923
C _L2f -0.2091 -0.1674 -0.1214 -0.1185 -0.1624
f 5.435 5.559 5.599 5.493 5.604
D _L12 7.151 4.781 4.973 5.151 6.13
5f ₁₂ -6.596 -10.839 -10.588 -7.253 -8.476
P _W12 0.340 0.270 0.277 0.229 0.313
f ₁ -7.934 -8.683 -9.179 -7.409 -8.983
R _L2f -4.783 -5.975 -8.236 -8.438 -6.158
f _2g 13.636 11.293 10.731 10.049 10.141
oal 36.008 35.000 35.000 35.000 33.800
f _1g -6.538 -10.839 -10.921 -7.253 -8.476
R _L1r 5.457 6.132 5.200 5.200 5.200
D _L23 0.100 0.100 0.100 0.100 0.100
f _Lf 16.176 19.054 17.196 19.104 18.579

Reference Signs List 1 mirrorless single-lens camera 2 body 3 lens barrel 21 CCD sensor 30 optical system 31 first lens group 32 second lens group 33, S aperture OA optical axis

Claims (14)

The optical system comprises, in order from the object side, a first lens group and a second lens group having positive refractive power,
The first lens group includes, in order from the object side, a first lens L1 having a convex surface facing the object side and negative refractive power, and a second lens L2 having a meniscus shape and a concave surface facing the object side,
The total number of lenses is 5 to 10, and
An optical system that satisfies the following equation:
1.837≦ (C _L1r - _{C L2f} )×f<2.55 (1)
0.860≦ D _L12 /f<5.00 (2)
1.809≦f2g _/ f<2.70 (7)
however,
C _L1r : Curvature of the lens surface on the image side of the first lens L1 C _L2f : Curvature of the lens surface on the object side of the second lens L2 f : Focal length of the optical system when focusing on infinity D _L12 : Distance on the optical axis between the lens surface on the image side of the first lens L1 and the lens surface on the object side of the second lens L2 when focusing on infinity
f2g : focal length _of the second lens group The second lens group is
Having an aperture,
The lens is composed of three or less lenses on the image side of the aperture stop, and
The optical system according to claim 1 , wherein the three or fewer lenses include a cemented lens of one lens having a positive refractive power and one lens having a negative refractive power. 3. The optical system according to claim 1, which satisfies the following formula:
-3.40<R _L2f /f<0.00 (6)
however,
R _L2f : radius of curvature of the object-side lens surface of the second lens L2 The optical system according to any one of claims 1 to 3 , which satisfies the following formula:
5.0<oal/f<8.0 (8)
however,
oal: total optical length of the optical system The optical system according to claim 1 , wherein the second lens L2 has a negative refractive power. The optical system according to any one of claims 1 to 5 , which satisfies the following formula:
-2.40<f _1g /f<-0.75 (9)
however,
f _1g : focal length of the first lens group The optical system according to any one of claims 1 to 6 , which satisfies the following formula:
0.50<R _L1r /f<10.00 (10)
however,
R _L1r : radius of curvature of the lens surface of the first lens L1 on the image side the second lens group has a pair of compound lenses on an image surface side adjacent to the aperture stop,
8. The optical system according to claim 1 , wherein the compound lens comprises one lens having a positive refractive power and one lens having a negative refractive power. The optical system according to any one of claims 1 to 8 , which satisfies the following formula:
1.70<N _L1 <2.00 (11)
however,
N _L1 : the refractive index of the first lens L1 at the d line the second lens group includes a third lens L3 having a positive refractive power,
The optical system according to any one of claims 1 to 9 , which satisfies the following formula:
1.60<N _L3 <2.00 (12)
N _L3 : the refractive index at the d line of the third lens L3 the second lens group includes a third lens L3 having a positive refractive power,
The optical system according to any one of claims 1 to 10 , which satisfies the following formula:
0.010<D _L23 /f<0.050 (13)
however,
D _L23 : the distance on the optical axis between the lens surface on the image side of the second lens L2 and the lens surface on the object side of the third lens L3 when the optical system is focused on infinity The optical system according to claim 1 , further comprising a final lens Lf having positive refractive power, the final lens being disposed closest to the image surface side of the second lens group. The optical system according to claim 12 , which satisfies the following formula:
1.5<f _Lf /f<4.5 (14)
however,
f _Lf : focal length of the final lens Lf An imaging device comprising: an optical system according to any one of claims 1 to 13 ; and an imaging element provided on an image plane side of the optical system, for converting an optical image formed by the optical system into an electrical signal.

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